The present invention is in the field of imaging systems. More particularly, the present invention provides an apparatus for clamping the trailing edge of a supply of recording media, such as a printing plate, on the external drum of an imaging system.
In external drum imaging systems, a movable optical carriage is commonly used to displace an image recording source in a slow scan direction while a cylindrical drum, having recording media mounted on an external surface thereof, is rotated with respect to the image recording source. The drum rotation causes the recording media to advance past the image recording source along a fast scan direction that is substantially perpendicular to the slow scan direction.
The image recording source may include an optical system for generating at least one imaging beam that is scanned across the surface of the recording media. Each imaging beam may be separately modulated according to a digital information signal representing data corresponding to the image to be recorded.
The recording media to be imaged by an external drum imaging system is commonly supplied in discrete, flexible sheets, hereinafter collectively referred to as xe2x80x9cprinting plates.xe2x80x9d Each printing plate may comprise one or more layers supported by a support substrate, which for many printing plates is a plano-graphic aluminum sheet. Other layers may include one or more image recording (i.e., xe2x80x9cimageablexe2x80x9d) layers such as a photosensitive, radiation sensitive, or thermally sensitive layer, or other chemically or physically alterable layers. Printing plates that are supported by a polyester support substrate are also known and can be used in the present invention. Printing plates are available in a wide variety of sizes, typically ranging, e.g., from 9xe2x80x3xc3x9712xe2x80x3, or smaller, to 58xe2x80x3xc3x9780xe2x80x3, or larger.
A cassette is often used to supply a plurality of unexposed printing plates to an external drum imaging system. The printing plates are normally supplied in stacks of ten to one hundred, depending upon plate thickness, and are stored in the cassette. A plate manager may be used to automatically and selectively unload and feed a printing plate from a plurality of different cassettes to the external drum imaging system for imaging.
Many clamping systems are available for holding the trailing edge of a printing plate on the external drum of an external drum imaging system. One commonly used type of clamping system, for example, employs a plurality of magnets to hold the trailing edge of a printing plate in place. An example of a magnetic trailing edge clamping mechanism is disclosed in U.S. Pat. No. 6,412,413, incorporated herein by reference. Although this type of trailing edge clamping mechanism is effective, it has several drawbacks. For instance, a magnet of the trailing edge clamping mechanism may break apart from impact loads during normal operational conditions. It this should occur, small pieces of the magnet may adhere to the surface of the external drum. Since this may adversely affect the quality of the imaging provided by the imaging system, the external drum must be carefully cleaned to ensure that all pieces of the broken magnet have been removed. The trailing edge clamping system must also be repaired. This requires that the external drum imaging system be shut down and serviced by a technician, which reduces the throughput of the imaging system (e.g., the number of plates/hour that can be imaged by the system).
The present invention provides an apparatus and method for clamping the trailing edge of a printing plate on the external drum of an imaging system.
Generally, the present invention provides a trailing edge clamping mechanism for securing a trailing end of a printing plate on an external drum of an imaging system, comprising:
a plurality of magnetic clamp sections, wherein each magnetic clamp section includes:
a body having a top portion and a pair of legs, wherein a bottom surface of each leg forms a clamping surface of the magnetic clamp section;
a plurality of apertures formed in the top portion of the body for receiving a corresponding plurality of lift pads of an actuating system;
a set of permanent magnets mounted to an underside of the top portion of the body; and
a cover for encapsulating and protecting the set of permanent magnets, wherein the cover includes a raised portion for accommodating the set of permanent magnets, and
a pair of flanges for securing the cover to the underside of the top portion of the body.
The present invention further provides an imaging system comprising:
an external drum for supporting a printing plate;
a system for recording image data onto the printing plate;
a leading edge clamping apparatus for clamping a leading edge of the printing plate on the external drum; and
a trailing edge clamping apparatus for clamping a trailing edge of the printing plate on the external drum, wherein the trailing edge clamping apparatus includes a plurality of magnetic clamp sections, and wherein each magnetic clamp section includes:
a body having a top portion and a pair of legs, wherein a bottom surface of each leg forms a clamping surface of the magnetic clamp section;
a plurality of apertures formed in the top portion of the body for receiving a corresponding plurality of lift pads of an actuating system;
a set of permanent magnets mounted to an underside of the top portion of the body; and
a cover for encapsulating and protecting the set of permanent magnets, wherein the cover includes a raised portion for accommodating the set of permanent magnets, and a pair of flanges for securing the cover to the underside of the top portion of the body.